package the.offer.DataStructure.Impl;

import the.offer.DataStructure.Interface.Queue;

public class LoopQueue<E> implements Queue<E> {
    private E[] data;
    private int front, tail;

    public LoopQueue() {
        this(10);
    }

    public LoopQueue(int capacity) {
        data = (E[]) new Object[capacity + 1];
        front = 0;
        tail = 0;
    }

    public int getCapacity() {
        return data.length - 1;
    }

    @Override
    public boolean isEmpty() {
        return front == tail;
    }

    @Override
    public int getSize() {
        return (tail + data.length - front) % data.length;
    }

    /**
     * 均摊复杂度：O(1)
     */
    @Override
    public void enqueue(E e) {
        if ((tail + 1) % data.length == front) {
            resize(2 * getCapacity());
        }
        data[tail] = e;
        tail = (tail + 1) % data.length;
    }

    /**
     * 均摊复杂度：O(1)
     */
    @Override
    public E dequeue() {
        if (isEmpty())
            throw new IllegalArgumentException("Cannot dequeue from an empty queue.");
        E ret = data[front];
        data[front] = null;
        front = (front + 1) % data.length;
        if (getSize() == getCapacity() / 4 && getCapacity() / 2 != 0) {
            resize(getCapacity() / 2);
        }
        return ret;
    }

    @Override
    public E getFront() {
        if (isEmpty())
            throw new IllegalArgumentException("Cannot dequeue from an empty queue.");
        return data[front];
    }

    private void resize(int newCapacity) {
        E[] newData = (E[]) new Object[newCapacity + 1];
        int size = getSize();
        for (int i = 0; i < size; i++) {
            newData[i] = data[(front + i) % data.length];
        }
        data = newData;
        front = 0;
        tail = size;
    }

    @Override
    public String toString() {
        StringBuilder res = new StringBuilder();
        res.append(String.format("Queue: size = %d, capacity = %d, front = %d, tail = %d\n", getSize(), getCapacity(), front, tail));
        res.append("Queue: ");
        res.append("front [");
        int size = getSize();
        for (int i = 0; i < size; i++) {
            res.append(data[(front + i) % data.length]);
            if (i + 1 != size)
                res.append(", ");
        }
        res.append("] tail");
        return res.toString();
    }
}
